I need do draw perpendicular lines at fixed intervals to a path. The path may be either open or closed. This is used as a symbol on maps to denote a depression with the perpendicular stubs pointing in the direction of the depression. Ideally, I would like the perpendicular lines to draw themselves as I draw the path. Ideas?

Or, if you actually prefer lines and intervals to be proportional, in other words being wider/narrower away from the path in curved paths, you may use a high Stroke Weight and Dashed Line; for the latter, up to CS5 you may use the free Adjust Dashes script available at